This application is based on Japanese Patent Application No. Hei 11-241468 filed on Aug. 27, 1999, the content of which is incorporated herein by reference.
1. Field of the Invention:
The present invention relates to an electromagnetic valve for a vehicular brake apparatus and a hydraulic circuit thereof.
2. Description of Related Art:
Conventionally, in a vehicular brake system, a pump is used for practicing several kinds of control methods such as a trace control (VSC), a traction control (TRC) and a brake assist control. The pump pressurizes a brake fluid from a master reservoir and supplies the pressurized brake fluid to a wheel cylinder. Additionally, a normally close type electromagnetic valve is used between the pump and the master reservoir for opening and closing a passage therebetween. For instance, FIG. 7 shows this kind of valve. A valve has a movable member 102 having a plunger 100 and a ball 101 which are welded integrally. Normally, a spring 103 pushes the movable member 102 in a direction A. Therefore, a fluid communication between a suction side of the pump and the master reservoir is closed by pressing the ball 101 on a seat surface 105 of a seat member 104. When a coil 106 is energized, the movable member 102 is attracted in a direction B, opens the connection.
However, in a case that a large pulsation is generated in a pressure P2, a pressure difference is generated between a front end and a rear end of the plunger 100. Therefore, the movable member 102 occasionally moves in direction B even though the coil 106 is not energized.
Such an unnecessary movement of the movable member 102 causes an unnecessary opening and lowers a controllability of the system.
The present invention addresses these drawbacks by providing an improved electromagnetic valve and a hydraulic circuit.
It is therefore an object of this invention to provide an electromagnetic valve for avoiding an unnecessary and undesired opening even if a pressure pulsation is generated.
It is a further object of this invention to provide a small electromagnetic valve.
It is another object of this invention to provide a hydraulic circuit having an electromagnetic valve in which an unnecessary and undesired opening is avoided even if a pressure pulsation is generated.
According to a first aspect of the present invention, a plunger and a movable member are made as independent members. The plunger is separated from the movable member to permit a free movement of the movable member between the plunger and the seat member. Therefore, if the plunger moves undesirably, the movable member can keep a closing condition in response to a pressure difference between a plunger side and a valve seat side.
The electromagnetic valve may apply to a hydraulic circuit, such as a brake fluid circuit for a vehicle. In this case, the electromagnetic valve is disposed between a suction side of a pump and a reservoir for supplying a brake fluid.